The system is a complex network of glands that release tiny amounts of hormones into the bloodstreams of humans and other vertebrate animals.

The endocrine system is a complex network of glands that release tiny amounts of hormones into the bloodstreams of humans and other vertebrate animals.

Explanation:

The endocrine system is a set of organs, tissues and cells whose function is to release various chemical substances called hormones into the bloodstream. The endocrine glands are the group of cells that produce and release hormones, which are secreted into the blood while waiting for the proteins that are designed to specifically capture each of them, are responsible for transporting them to the cells of the tissues and organs to which they must reach. Once there, they transmit the precise orders to regulate cellular activity.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.